Spread to the western hemisphere
HIV-1 strains are thought to have arrived in the United States from Haiti in the late 1960s or early 1970s. HIV-1 is believed to have arrived in Haiti from central Africa, possibly through professional contacts with the Democratic Republic of the Congo.
Because of the long incubation period of HIV (up to a decade or longer) before symptoms of AIDS appear, and because of the initially low incidence, AIDS was not noticed at first. By the time the first reported cases of AIDS were found in large United States cities, the prevalence of HIV infection in some communities had passed 5%. Worldwide, HIV infection has spread from urban to rural areas, and has appeared in regions such as China and India.
 Canadian flight attendant theory
A Canadian airline steward named GaŽtan Dugas was referred to as "Patient 0" in an early AIDS study by Dr. William Darrow of the Centers for Disease Control. Many people consider Dugas to be responsible for bringing HIV to North America. This is considered inaccurate, as HIV had spread long before Dugas began his career. This rumor may have started with Randy Shilts' 1987 book And the Band Played On (and the movie based on it, in which Dugas is referred to as AIDS' Patient Zero), but neither the book nor the movie state him to have been the first to bring the virus to North America. He was called "Patient Zero" because at least 40 of the 248 people known to be infected by AIDS in 1983 had had sexual intercourse with him, or with someone who had sexual intercourse with him.